The present invention relates to a filter for separating suspended solids from a liquid and, more particularly, for a filter which can be used for separating a juice or sap from solids.
Filters can be used to separate solids in suspension within liquid products, particularly to separate insoluble solids from soluble solids and liquids in a suspension, like citric juices, and which has been developed to carry out the filtering process and to also provide for the simultaneous separation of juice sap (brix) and a self-cleaning effect on the filtering sleeve by rinsing.
Generally the filter is also provided with a device to enable the filtering sleeve to absorb overpressures resulting from the filtering process dynamics and a device to enable quick assembly/disassembly to effect possible maintenance.
The filter can be associated with a circuit for one or more filters, providing for: feeding of product to be filtered, removal of the filtered material, removal of solids, counterwashing and filter cleaning operations. The circuit can incorporate a safety device against eventual disruption of the filtering sleeve and devices enabling the filter to work in an open or closed circuit, all with the purpose of meeting the needs of interested parties for this kind of equipment.
A filter to separate liquids from solids is already known and essentially comprises a filter body, of which an end includes the outlet for the product to be filtered; the intermediate region of said body holds a set comprising: a filtering element with cylindrical tube screen shape, which inlet communicates with the inlet of the filtering body and a rotor within the filtering element operated by a driving set which promotes the circulation of product to be filtered. In its lower part, the middle region of the body provides an outlet for the filtered material. The opposite end of said body provides the outlet for solids, with which the outlet of the filtering element communicates. The body is assembled on a rack by means of a device to regulate its inclination.
The rotor is provided with an entry path equipped with a turbine imparting axial movement to the product being fed and a processing path equipped with flat radial blades imparting radial movement to the liquid, so that it can go through the filtering element.
Finally, the rotor may include a cleaning device for the filtering element, comprising a helix-twisted wire around processing radial blades, staying near the internal face of the filtering element, mechanically dragging the solid material retained in the filtering element until it is fully withdrawn.
The use of this filter has few drawbacks. When the liquid comes from the inlet stage to rotor processing, the axial hydrodynamic impelling force is largely reduced, so that the liquid is concentrated and most of it goes through the initial region of the filtering element. This subjects the filtering element to different forces and, depending on the material with which it is manufactured and the magnitude of such forces, elastic deformation may occur, thus compromising a better performance of said filtering element.
As a consequence, only a small part of the filtering element effectively acts to process the material.
A first object of the invention is therefore to eliminate the problems with earlier filter.
This object is attained with a filter unit which comprises:
a filtering sleeve made of technical material (canvas) communicating with the inlet and outlet of the filter body; and
a turbine with two helicoidal paths, namely, a short helix-shaped inlet path, located in an inlet chamber of the filter body and imposing axial thrust and no radial thrust to the liquid, and a long helix-shaped processing turbine path, located inside the filtering sleeve. The processing path is equipped with blades with convex trailing surfaces keeping an appropriate spacing (gap) relative to the filtering sleeve and imposing highly intense radial thrust and low axial thrust to the liquid, so to displace it according to a vortex inside the sleeve.
This kind of filter construction solves the drawbacks of the usual one, since the loss of hydrodynamic thrust between both turbine paths is minimized, thus avoiding the concentration of liquid in the beginning of the sleeve and eliminating the different forces which can cause elastic deformation and loss of efficiency. This construction also provides that the whole surface of the sleeve acts effectively during processing. Another effect provided by the turbine, as described above, is the running out of the liquid along the internal surface of the filtering sleeve before passing through it, which means that it drags the solid material towards the exit. This provides a hydrodynamic self-cleaning effect by means of simultaneously rinsing the filtering sleeve while filtering. This kind of self-cleaning of the sleeve prevents the solid material from being compressed against it, possible crushing of said material, clogging of the sleeve, as in conventional filters.
Usually, and especially while processing citric juices, the pulp resulting from separation processes effected with usual filters still contains soluble solid material (brix), constituting the best part of the product being processed. Separation of the soluble solid material from the insoluble solid material while using conventional filters can only be done in appropriate equipment, located downstream from the filters in a processing line. This is undesirable, since it requires the additional equipment to extract brix, means to circulate the pulp from the filters to such equipment, etc. Besides the need for the additional equipments per se, it also requires that additional process stages be provided, thus adding complications and costs to the process.
The present filter can overcome such problems. For that, the filter includes a circuit to separate brix, comprising radial nozzles provided within the turbine axis, which inject pressured water, radially crossing the liquid being filtered and the solid material retained in the sleeve, while separating brix.
The circuit solves the problems occurred when using conventional filters, since it eliminates the need for specific equipment and process stages to separate brix downstream from the filters, as usually occurs. Optionally, the brix separator device has the radial nozzles in the axis and/or injecting nozzles provided in the framework injecting pressured water in the outlet region for solids in the filtering sleeve.
The flat profile of blades of the conventional filters generates relatively high resistance strength to rotor movement, thus requiring the use of sufficient engine power to rotate the rotor, drag the liquid to be processed and overcome the resistance. This results in the need for a relatively high power motor, which is undesirable.
The helicoidal profile of turbine blades of the present filter and their spacing from the filtering element provides for lower resistance, thus enabling the use of lower power motors in comparison to conventional filters with flat blades.
Another feature of a conventional filter is that its filtering element is fixed to the filter body. Therefore, when the filtering element is subjected to forces incurred from the filtering process dynamics, its stretches, is subject to elastic deformation and compromises its filtering capacity and/or, in extreme cases, can also suffer irreversible deformation or rupture.
The filter of the invention overcomes this problem in part in that the liquid flows as a vortex, thus minimizing the direct impact against the sleeve. The filtering sleeve of the filter of the invention sealed on a resilient support, keeping it stretched under normal internal pressure conditions, allowing it to axially contract and radially expand when internal pressure increases. Therefore, the filtering sleeve absorbs the forces without suffering significant elastic deformation, keeping its filtering ability as pressure increases. When the pressure peak is over, the resilient support allows the sleeve to return to its normal configuration.
Another problem caused by conventional filters, when equipped with a filtering element in the form of a steel screen, is that the openings of the filtering element define cutting edges, near which free edges of the rotor flat blades pass. The joint action of said edges of the filtering element and the free edges of rotor blades while moving facilitates smashing of most of the solid part of the material to be processed and fragments go through the filtering element, thus creating a cloudy filtered product still containing fragmented solids, which is undesirable. The filtering elements in the form of a steel screen can still provide for external reinforcing bars. This fact, in combination with other features of the steel filtering element and the filtering process dynamics itself can produce turbulence in the material being processed, thus facilitating the incorporation of air and some opacity, which is undesirable.
This problem is overcome by the invention since the filtering sleeve is made of a fabric (canvas) with round section wires, thus avoiding the cutting edges. The lack of edges and some flexibility of the wire constituting the sleeve eliminates the tendency for the processed material to be fragmented and the incurred problems, as explained above. The circular section of the wires also facilitates a certain Venturi effect, which contributes to passing the liquid phase of the material through the sleeve.
Another problem with a conventional filter is that, depending on the concentration of the retained solid material, the twisted-wire cleaning device presses the retained solids against the filtering element, which may cause blockage and apply additional forces to the filtering element thus straining the equipment. The solid phase of the material can be crushed and consequently the quality of the final filtered product reduced.
This drawback is overcome by the self-cleaning effect by rinsing as provided by the turbine of the present filter, as described above.
Due to the characteristics of the filtering process as effected by that kind of filter, periodical cleaning and eventual maintenance operations of the filter are necessary, thus requiring interruptions.
The present filter reduces cleaning and maintenance interruptions as much as possible. To that effect, the filter includes a range of devices intended for quick assembly/disassembly. The filtering sleeve and its resilient support are assembled one next to the other, so to constitute a monoblock set. The filter body also includes a removable cap provided at its outlet end for solids. The cap and the opposed end of the filter body provide ring surfaces for the connection of the filtering sleeve. The body cap is provided with a removable bearing housing for the turbine axis and the opposed end of the filter is provided with an axis support. The lower part of the filter body and the filtering sleeve and support set are provided with parts of a support and sliding guiding device for the sleeve/support set. Assembled on the filter body, a rail set is provided, on which the cap and subsequently the sleeve and support set can be suspended or vice versa, to assembly/disassembly the filter. These devices when jointly working provide for quick assembly/disassembly of the filter, thus reducing the interruption period for eventual maintenance operations. On the other hand, the filter is provided with an associated set, essentially comprising: inlet tubes for the product, an outlet for the filtered product, an outlet for solid material, devices water and counterwashing solution injection; a set of automatic control and drainage valves for various lines of the flow circuit; motor-pump sets; a safety device against filtering sleeve disruption and a computerized device (PLC) for the command of the valves and pumps, among others, performing the filter set cleaning operations in a quick and efficient way.
The invention also includes the assembly of a processing unit for liquids, which may consist of one or various filters working in an open or closed circuit, so to meet as many needs as possible from the interested parties in this kind of equipment.